Colossal magnetoelectric effect induced by parametric amplification

We describe the use of parametric amplification to substantially increase the magnetoelectric (ME) coefficient of multiferroic cantilevers. Parametric amplification has been widely used in sensors and actuators based on optical, electronic, and mechanical resonators to increase transducer gain. In our system, a microfabricated mechanical cantilever with a magnetostrictive layer is driven at its fundamental resonance frequency by an AC magnetic field. The resulting actuation of the cantilever at the resonance frequency is detected by measuring the voltage across a piezoelectric layer in the same cantilever. Concurrently, the spring constant of the cantilever is modulated at twice the resonance frequency by applying an AC voltage across the piezoelectric layer. The spring constant modulation results in parametric amplification of the motion of the cantilever, yielding a gain in the ME coefficient. Using this method, the ME coefficient was amplified from 33V/ (cmOe) to 2.0 MV/(cmOe), an increase of over 4 orders of magnitude. This boost in the ME coefficient directly resulted in an enhancement of the magnetic field sensitivity of the device from 6.0 nT= ffiffiffiffiffiffi Hz p to 1.0 nT= ffiffiffiffiffiffi Hz p . The enhancement in the ME coefficient and magnetic field sensitivity demonstrated here may be beneficial for a variety actuators and sensors based on resonant multiferroic devices.VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4935332]